Replenishing ground water

Groundwater project is at the forefront of water purification

Above; The 13-mile groundwater replenishment system pipeline is now under construction between Fountain Valley and Anaheim, Calif. Photos: Orange County Water District Below: OCSD and OCWD staff reviewing plans for the groundwater replenishment system backed up by a state-of-the-art ultraviolet light unit. Shown are Virginia Grebbien (left), OCWD general manager; Mike Markus, GWR system program manager; and Blake Anderson, OCSD general manager.

This Phase One GWR system microfiltration unit is on the OCWD campus in Fountain Valley, Calif. Microfiltration is the first step in the Phase One purification process that is now producing 5 mgd for the seawater intrusion barrier.

Despite the recent dramatic rains in California. Orange County remains in the midst of a prolonged drought affecting the entire Western United States. And with projections for large population increases of up to 500,000 people by 2020, combined with other environmental and political factors, Orange County's water supplies are being challenged.

Nearly a decade ago, the leaders of the Orange County Water District (OCWD) and Orange County Sanitation District (OCSD) in Fountain Valley recognized the need for a new reliable water source, a more effective barrier to prevent seawater intrusion, and a reliable supply of water to recharge groundwater sources. These agencies also knew that without some changes the amount of treated wastewater being sent to the ocean would soon outpace the capacity of the existing ocean outfall pipeline and lead to the need for a second pipeline to accommodate peak flows.

This foresight led the county to propose a new water purification project to achieve all its objectives. The $487 million groundwater replenishment (GWR) system will be the largest water purification project of its kind in the world, and will build on the county's legacy as a leader in water purification and reuse. Under construction since 2003, the project uses a three-step process—micro filtration, reverse osmosis, and ultraviolet light with hydrogen peroxide disinfection—to purify highly treated wastewater. This process is the same as that used to purify baby food, fruit juices, medicines, and bottled water.

When completed and operational, half of the water from the GWR system will be injected into Orange County's seawater intrusion barrier through 36 injection wells. The remaining water will be piped to spreading basins, where it will take the natural path of rainwater as it filters through clay, sand, and gravel into the groundwater aquifer. The purified water will blend with the county's other sources of water and augment groundwater supplies for north and central Orange County residents—enough to meet the needs of 144,000 families. In addition, the project will delay, possibly indefinitely, the need for another ocean outfall because there will be less water going to the ocean. There are three main components of this project currently under construction: the Advanced Water Purification Facility (AWPF), a 13-mile pipeline connecting the AWPF to OCWD's groundwater recharge basins, and expansion of the existing seawater intrusion barrier with additional injection and monitoring wells.

A Successful Partnership

For more than 25 years, the OCWD and OCSD have cooperated to create clean, pure water from highly treated wastewater at Water Factory 21, a facility built to provide water for a now-inadequate seawater intrusion barrier. Water Factory 21, a model for water purification around the world, was recently demolished to make way for the GWR system. The two agencies are splitting capital costs for the system, but OCWD maintains responsibility for managing construction and, eventually, for operating and maintaining the system. This unique arrangement works because both agencies benefit from the project and have established effective ways to communicate.

Weekly general manager meetings keep both agencies updated on the project's status. Both agencies are actively engaged in the project, and work together to find creative solutions to challenges when they arise. A joint steering committee features three board members from each agency. That committee, which met twice a month during the design phase of the project and now meets once a month during construction, reviews all decisions before they go to the boards of each agency. OCSD has a 25-member board and OCWD a 10-member board—involvement of board members on the steering committee keeps each agency's board informed and streamlines the decision-making process.

To simplify the complicated design process, the GWR team chose to pre-qualify and pre-purchase the new technology at the heart of the system—microfiltration and ultraviolet light purification equipment. Often, the contractor will choose the equipment manufacturer for a project, based on the specifications provided. However, because the microfiltration and ultraviolet light purification technologies were new and manufacturers scarce, the size and shape of the equipment was not standardized. This presented a challenge to the design team: they needed to know the characteristics of the units to develop a design that allowed the technologies to work together within a single system. By pre-qualifying and pre-purchasing the technology, the size, shape, and layout were no longer unknowns.

To pre-qualify the equipment, each manufacturer submitted its technology to a six-month pilot test to prove that it could meet the performance specifications before being allowed to bid on the project. Qualified manufacturers submitted bids that were reviewed based on life-cycle costs and the winning manufacturer agreed to a locked-in price. The contractor was then authorized to purchase the equipment from the manufacturer at that price.

The AWPF features a Delta V process control system from Emerson, Austin, Texas, which also required an intense review process. The fiber optic-based Delta V system—often used in industrial plants-contains numerous redundancies, making it more reliable than typical supervisory control and data acquisition (SCADA) systems. While the decision to purchase and deploy a new process control system during the design of the GWR system added to the overall complexity of the project, the engineers decided that the Delta V system was an emerging technology that would make the GWR system a model for future water purification plants, and worth the investment.